1. Field of the Invention
The present invention relates to a process for deasphalting an asphalt-containing mineral oil. More specifically, the process relates to the preparation of lubricating oils having a low asphalt content. Still more specifically, the process comprises contacting an asphalt-containing hydrocarbon feedstock with a deasphalting solvent.
2. Description of the Prior Art
Propane has been used extensively in deasphalting asphalt-containing hydrocarbon feedstocks, especially in the preparation of high quality lubricating oils. The use of propane has necessitated elaborate solvent cooling systems utilizing cold water, which is a relatively expensive cooling agent. While it is desirable to use alternative cooling equipment such as air fin coolers, this has not always been possible in the case of propane deasphalting in locations where ambient air temperature reaches about 100.degree.F. This is due to the fact that relatively low extraction tower temperatures are required (e.g. 110.degree.F. extraction tower bottoms temperature with an Aramco vacuum residuum) to achieve satisfactory yield and quality of deasphalted oil, thereby resulting in poor heat exchange.
Thus, attempts have been made in the past to develop a solvent system useful in deasphalting processes, which would allow operation at elevated temperatures relative to conventional propane deasphalting temperatures, thereby permitting easy heat exchange in those instances where the utilization of air-fin cooling techniques are preferred. In addition, it would be desirable to integrate dewaxing operations with deasphalting operations by having a common solvent recovery system.
Typical of prior art deasphalting processes is the process described in U.S. Pat. No. 2,337,448 in which a heavy residuum is deasphalted by contacting it at elevated temperature with a deasphalting solvent such as ethane, ethylene, propane, propylene, butane, butylene, isobutane, and mixtures thereof. In the process of this patent may be utilized such other solvents as pentane, gasoline, mixtures of alcohol and ether, acetone and other solvents capable of dissolving the oil and resins but not the asphaltenes.